Active/fit 46 year old. my glute muscle was twitching like crazy while sitting on the couch. no pain. felt like a little drummer was using my butt as a drum. it lasted continuously for ~10 minutes. is this concerning? early sign of something bad?

Not necessarily bad: This could simply be an irritable superficial nerve causing muscle twitching which should resolve. It may have to do with recent athletic or occupational activity. Sometimes caffeine is a cause. Serious symptoms would be widespread muscle twitching which can be caused by deficiencies of calcium, magnesium or electrolyte imbalance. See your MD or a neurologist if symptoms persist.